Photolithography techniques are used for fabricating components used in integrated circuits, such as metal-insulator-metal (MIM) capacitors. The MIM capacitors are essentially built-up by forming a multitude of components in a number of layers, one layer on top of another. FIG. 1 illustrates a conventional MIM capacitor 2. The formation processes include forming a bottom metal layer, a top metal layer and an insulation layer therebetween, and etching the top metal layer and the insulation layer to form a top metal plate 10 and an insulator 12, respectively.
It is necessary to ensure that the components in capacitor 2 are accurately positioned and formed. As components get smaller, it is necessary to position and form components to increasingly finer tolerances. For geometries of 0.18 microns and less, accuracy is improved by applying an anti-reflective coating (ARC) layer 16, such as silicon oxynitride (SiON), to the metal layer prior to patterning the bottom metal layer. The ARC layer 16 reduces reflection from the metal layers, allowing more accurate alignment for the formation of the bottom metal plate 14.
In the prior art, the ARC layer 16 is typically not removed because of difficulties in removal processes, thus it remains a part of the MIM capacitor 2.
The ARC layer 16, however, is typically electrically weak and is prone to current leakage and electrical breakdown. For example, a physical void 18 may be formed between the MIM capacitor 2 and a neighboring conductive component 20. The void 18 typically also reveals the path of the leakage current. A leakage current that flows between the top metal plate 10 and the bottom metal plate 14 may occur in regions 22 in the ARC layer 16, so that a breakdown occurs at a low voltage, causing the MIM capacitor 2 to fail.
Accordingly, what is needed is a method that can be used for fabricating MIM capacitors with improved electrical performance. For example, it is desirable to be able to fabricate MIM capacitors that have higher breakdown voltages and reduced leakage currents. It is also desirable to be able to fabricate MIM capacitors for which the variability of these parameters is reduced; that is, it is desirable for the range of values of breakdown voltage and leakage current to fall within a tighter tolerance band. The present invention provides a novel solution to these needs.